Various communication standards, such as digital subscriber line (xDSL), very-high-bit-rate digital subscriber line 2 (VDSL2), G.hn, and G.fast, have been proposed or developed to provide high-speed data transmission from the service provider (e.g., a central office) to a customer premise over the existing twisted-pair copper wiring conventionally used for telephone service. Such technologies leverage modem technology to increase the data transfer bandwidth of the twisted-pair copper wiring. Typically, modems are provided on the ends of the subscriber line copper wiring to communicate between the central office and the customer premise. The manner in which the two modems communicate is established by the particular standard governing the communication. Because the existing telephone wire is used, the data signals are typically transferred out-of band with the voice band signals. Because different frequencies are used for the voice band and the data band, voice and data information can be concurrently transferred over the twisted-pair copper line.
Service providers have increased data bandwidth by installing fiber optic cabling between the central office (CO) and a distribution point unit (DPU) closer to the customers. A particular DPU may interface with a bundle of twisted pairs to service a relatively small number of customer premise connections. This approach shortens the length of the copper pair between the CO interface at the DPU and the customer, thereby allowing increased data rates. Thus the DPU will provided telephony and/or data to one or more customer premises equipment (CPE)
One difficulty arising from an optical connection between the central office and the DPU lies in the inability to provide a source of power for the DPU. Due to the remoteness of the DPU with respect to the central office, a local power supply is often unavailable or expensive to install.
Power for a DPU may be provided by reverse power feeding, wherein power is supplied to the DPU from the various CPEs for which telephony and/or data services are provided from the DPU. A standard for reverse power feeding is being standardized by ETSI and the Broadband World Forum. In such an embodiment, a power supply in the DPU may combine power contributions from multiple CPEs to power a main distribution unit (MDU) that handles the voice and data communication. This arrangement is referred to as a reverse power system, since the CPEs are the power sourcing equipment (PSE) and the DPU, particularly the MDU, is the powered device (PD).
The CPE PSE thus injects power across the copper pair. In order to use a plain old telephony service (POTS) type analog telephone, a POTS adapter is to be installed between the copper pair and the POTS telephone. FIG. 1 illustrates a high level block diagram of such a reverse power feeding arrangement 10, reverse power feeding arrangement 10 comprising a DPU 20 and a CPE 30 connected by a copper pair 40, with certain standard ETSI symbols shown. DPU 20 comprise a data provision module 50, typically in optical communication with a CO; a DC extraction circuitry 60; a distribution point power supply 65; and a classification current circuitry 67. Data provision module 50 and DC extraction circuitry 60 are each connected to copper pair 40 past the U-O reference point. The U-O reference point is defined as the reference point at the DPU containing both DC power and service data. Distribution point power supply 65 is arranged to convert power received from DC extraction circuitry 60 to an appropriate power for data provision module 50, and other devices located within DPU 20. Classification current circuitry 67 is coupled to the output of DC extraction circuitry 60.
CPE 30 comprises a PSE 70, a power splitter 80, a service splitter 90, a POTSA-D adaptor 100 and a POTS telephone 110. PSE 70 is connected to power splitter 80 across the U-R2P reference point, defined as the reference point at CPE 30 containing the injected DC power. Power splitter 80 is connected to service splitter 90, which provides service and optionally analog phone service for CPE 30. Power splitter 80 is additionally connected to copper pair 40 across the U-R reference point, defined as the reference point at CPE 30 containing both DC power and service data. POTSA-D 100 is connected to copper pair 40 between power splitter 80 and the U-R reference point across the U-R2S reference point, defined as the CPE reference point containing the baseband POTS and the converted POTS signaling. POTSA-D 100 is an adapter that can be attached to one or more POTS telephones 110 in CPE 30. POTSA-D 100 is arranged to perform the following functions: translate the signals from the upstream DC and low frequency POTS signaling from the POTS telephone 110 into an in-band or out-of-band signaling system; translate the signals from the downstream in-band or out-of-band signaling system into POTS signaling towards the POTS telephone 110; and provide sufficient current, with a current limit, and DC voltage to supply POTS telephone 110.
In order to provide more efficient reverse power feeding, it is advantageous for PSE 70 to determine the class of DPU 20. Particularly, in a classification stage, PSE 70 is arranged to generate a classification voltage, which is presented to DPU 20, and classification current circuitry 67 is arranged to generate a classification current whose magnitude is indicative of the class of DPU 20. PSE 70 is then arranged, responsive to the magnitude of the received classification current, to determine the class of DPU 20 and adjust the current limit accordingly.
In the event that POTS telephone 110 is mistakenly connected to the reverse power feeding network without POTSA-D 100, i.e. POTS telephone 110 is mistakenly connected directly to the in-premises wiring at the potential of reference point U-R, when POTS telephone 110 is off-hook it draws a current from PSE 70. If POTS telephone 110 goes off-hook during, or before, the classification stage of DPU 20, PSE 70 will read the combination of the classification current and the current drawn by POTS telephone 110, instead of just the classification current. As a result, PSE 70 will read an incorrect current magnitude, which may alter the perceived class of DPU 20. For example, in one embodiment classification current circuitry 67 is arranged to generate, in response to a classification voltage of 14.5-20.5 V: a classification current of 9-12 mA for a class 1 DPU 20; a classification current of 17-20 mA for a class 2 DPU 20; and a classification current of 26-30 mA for a class 3 DPU 20. Assuming DPU 20 is a class 2, classification current circuitry 67 will thus output during the classification stage a classification current with a magnitude of 17-20 mA. If an off-hook POTS telephone 110 is represented by a resistor and zener diode circuit of 7.5 V and 1 kΩ, and PSE 70 generates a classification signal with a voltage of 17.5 V, then the off-hook current of POTS telephone 110 will be: (17.5V−7.5V)/1 kΩ=10 mA. Thus, instead of reading a classification current with a magnitude of 17-20 mA, PSE 70 will read a current of 27-30 mA and mistakenly determine that DPU 20 is a class 3 instead of a class 2. PSE 70 will thus provide the wrong current limit for DPU 20 and may also violate safety regulations which are set for class 2 devices.